A recent paradigm shift in public housing policy is catalyzing one of the largest planned migrations in US history. Public housing agencies are relocating residents of spatially concentrated complexes to voucher- subsidized rental units in the private market that are geographically dispersed. The HOPE VI policy embodies this paradigm shift, and is relocating 200,000 households from concentrated complexes to rental units in target cities. HOPE VI migrants tend to move to safer, less poor, and less drug-involved neighborhoods (though gains are attenuated for alcohol and other drug [AOD] abusers); at the same time, migrants' social networks and social supports decline. Migrants' neighborhood conditions, networks, and supports may evolve for some time: HOPE VI inaugurates a period of serial moves for 50% of migrants. Most migrants are African-American and all are poor. Rates of AOD abuse and HIV risk are high among these residents before they move. At issue in the proposed study is whether and how HOPE VI relocations, and the changes in migrants' neighborhood conditions, networks, and social supports that these relocations create, shape African-American migrants' AOD abuse and HIV risk. The proposed [4]-year study will have a quasi-experimental pre-/post-exposure design with an unexposed comparison group. The exposed group will consist of [180] migrants from 7 Atlanta Housing Authority (AHA) complexes targeted by HOPE VI; the unexposed comparison group will consist of 150 residents of 6 AHA complexes that are not relocating. All participants will be African-American, and we will seek variation in the sample in baseline AOD abuse status in order to study how AOD abuse shapes trends in outcomes of interest. The proposed multilevel longitudinal study, led by a new investigator, will achieve the following aims: Aim 1: Characterize trends in residential mobility among HOPE VI migrants during the [4]-year the study period; describe changes in the characteristics of the census tracts where migrants live over time (e.g., poverty rates); and learn how AOD abuse status affects these trends. Aim 2: Characterize changes in network and social supports over time in the full sample (N=[330]), and determine how HOPE VI status and AOD abuse status affect these changes. Aim 3: Describe trends in AOD abuse, proximal HIV risk factors, [and HIV incidence] over time in the full sample, and learn how these trends relate to HOPE VI status and AOD abuse status (where AOD abuse trends are not the outcome). Aim 4: Analyze relationships of changes in the characteristics of the census tracts where participants live (Aim 1), and in their networks and supports (Aim 2), to trends in AOD abuse and proximal HIV risk (Aim 3). This study will build on foundations laid by a NIDA R21 study in which we are (1) creating the [330]-member cohort; (2) initiating data collection; and (3) refining retention methods. Results will advance scientific knowledge in NIDA priority areas on migrations, AOD abuse, and HIV, and on determinants of AOD use and HIV among African-Americans.